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Thread: Stan_Ham diode driver (analog)

  1. #71
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    Quote Originally Posted by FourDee View Post
    So why doesn't anyone use this kind of driver?
    The high speed communications guys do.

    Most of the rest of the industry is just too cheap to use anything other then the simple opamp/pass transistor combo. Ie they don't like paying for opamps that can have inputs that can swing rail to rail etc Besides, most people coming out of EE school today are taught mainly digital , not analog and the idea of using a Howland current pump as a VCCS ie voltage controlled current source is in the Burr Brown etc app notes, not the basic EE textbooks.

    Basic electrical engineering texts are rarely good at showing how to do applied electronics.
    And EE professors are rarely interested in analog, and thus are unlikely to want student labs covering it. Thus only after a few years of field experience do you get good analog EEs. And good analog EEs are usually too highly sought after to be messing with laser drivers. Unless you send your kid to MIT, Perdue, Carnegie, Case, or similar schools, where learning this stuff is part of the culture and tradition.

    Bill, at his skill level, could be a gazillionaire designing chips, / but he likes to run his own company. For those of us who work with lasers, be glad he chooses this sacrifice and that he is happy doing it!

    Then you get the Dr Lava's, Uncle Worms, and the guys like me, who are forced to learn analog in order to do our jobs, as rarely in the research business does a off the shelf hardware exist for what you want to do.

    If you think ESD is spooky , wait till you try RF above 2 ghz. Despite my sarcasm in the previous post, I too want some lasorbs, and they cannot come soon enough.

    I might flip one on some test gear for a lark, in order better understand the device, but I need the things ASAP to go into something being prototyped for "our" boys and girls in the "stans" and have enough other development projects right now.

    I also suspect it might be useful in " impulse" generation, for another area of my interests.

    Steve
    Last edited by mixedgas; 01-21-2009 at 13:45.

  2. #72
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    Quote Originally Posted by The_Doctor View Post
    Oh man, 'negative resistance'! At this point I need to put my seething neurons to bed.
    Negative resistance does not exist, it is a poorly chosen term. A so called negative resistance device will ALWAYS be limited by some external factor, usually power supply impedance, so its not truely negative.

    Steve

  3. #73
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    riggered the gate, latching the SCR to keep the LED on. Longer nudges let that cap discharge so fast nonlatching worked too. Timing was critical, as was the quality of the switch, and better ways exist. Still nice though, it consumed zero current when off, unlike most schemes. Nothing to do with the subject here, but it was enough to make me think about SCR triggering, but didn't help me figure out the unlatching. Maybe it will, maybe it won't....

    End quote.

    I used a scr as a 1 bit memory, for a laser game rifle simulation, was that clip loaded into a rifle before? If SCR powered from .5 farad cap is not set, give user 100 new rounds. Then set SCR. Bulletproof system, worked great.

    Steve

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    Quote Originally Posted by mixedgas View Post
    Negative resistance does not exist, it is a poorly chosen term.
    I know, that's why I get a funny reaction whenever I encounter it.

    Then set SCR. Bulletproof system, worked great
    That's what I like about them too. I wanted to be sure than only user operation on the provided switch was capable of switching that flashlight on or off. Even the best new ones still have the same dreadful erratic contacts in the circuit as old crappy ones, once they've been in use a few days. Using an LED with constant current regulator and an SCR switch and a small induction coil in its base like used for rechargeable toothbrushes, a flashlight could be almost perfectly reliable. A slightly less efficient regulator would be a small payoff in many situations. Despite all this, the ONLY flashlight switched by SCR that I've seen or even heard of was the one I made. All the more shocking because all I did was use the most basic SCR teaching I learned when I first heard of them. In some ways it provides nothing unusual, I guess, but it does allow ultrastable latching operation with the simplest possible (nonlatching) switch. I'll find the circuit and post it in the 'other light sources' thread, someone might want to try it.
    Last edited by The_Doctor; 01-21-2009 at 23:18.

  5. #75
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    Quote Originally Posted by The_Doctor View Post
    I favoured varistors at least for protecting the supply regulator lines rather than the diode itself, but Robin Bowden insisted that a zener would be a better way. There was a little more to it, and I forget exactly what (minimal RC filtering I think, to trap what the zener didn't), but he showed me a video of a laser diode being wilfully zapped with sparks and looking as if it liked it. In fact, the sparks made it lase in flashes when it wasn't powered. I think I lost a load of saved emails, but if I do find that one I'll post details. Robin, if you're lurking, any chance you can post on this? I'll try hunting for that saved mail tomorrow, too late now though.
    Joining this thread kind of late but here is the clip for the "ESD powered" laser.
    http://die4laser.com/Misc-pics/ESD.mpg
    Robin.
    Lasers and beer don't mix. After 2 beers I lose coherence.

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    Quote Originally Posted by uk-laser View Post
    Joining this thread kind of late but here is the clip for the "ESD powered" laser.
    http://die4laser.com/Misc-pics/ESD.mpg
    Robin.
    That's an interesting video, but it's not fully explanatory to the viewer. At least I have questions when watching it. For example: That which is inside the little metal cylindrical case is not just a laser diode, right? There's more inside the little case, such as a laser diode driver, right?

    I only ask because it appears to me as though you are powering it with 4.5 volts worth of batteries.

    Bill

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    Wink

    Quote Originally Posted by Pangolin View Post
    There's more inside the little case, such as a laser diode driver, right?
    Saw right through me

    There is no driver as such just a 12R resistor, a TVS diode and a small cap.
    This "3 terminal" approach lets you get away with the higher clamping voltage of a TVS. Of course if I was building it now I would be using a Lasorb

    By the way what is the maximum supply voltage (diode Vf) of the Lasorb.
    It occurs to me that whilst the Lasorb will fully protect the LD from static whilst connected to or disconnected from the driver it does not protect in the case where the driver itself is damaged by ESD causing the driver to output an abnormal (excessive) drive current.

    I guess a Lasorb is in order on the driver modulation input and perhaps on the driver supply rail?
    You might be able to sell 3 times as many!

    Robin.
    Lasers and beer don't mix. After 2 beers I lose coherence.

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    whilst this has run off track I thought I would pull it back towards the orignal driver by posting a few questions;

    Firstly, im trying to complete a parts list and am hoping somebody can look through the objects and maybe help me out on the things im not entirely sure on.


    1. 2x 100 nf Capacitor 10-1780 £0.12
    2. 3x Diode 1N4148 47-3308 £0.008
    3. LM358 (N?) 82-0258 £0.22
    4. An Led (see below)
    5. 2x RTRIM64W Resistor. see below
    6. 7x10k resistor (multipack) £2.28
    7. BD437 81-0102 £0.18
    8. 1 x Some resistor
    9. 1 x 1k Resistor 62-6352 £0.70 for 10
    10. 1 x 1R Resistor 62-6320 £0.70 for 10
    11. 6V PSU

    4. - I assume that any ordianry LED will do, unless theres something ive missed.

    5. I need help on these, im hoping these will work

    8. As I dont know what diode I will be getting this remains some, but specifically how do you calculate the value of this resistor?

    Im intending to make this on strip board which involves me figuring out all the connections. If somebody has a plan the that would be cool. Otherwise im going to try make one myself.

    Silent

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    Quote Originally Posted by SilentShaddow View Post
    whilst this has run off track I thought I would pull it back towards the orignal driver by posting a few questions;

    Firstly, im trying to complete a parts list and am hoping somebody can look through the objects and maybe help me out on the things im not entirely sure on.


    1. 2x 100 nf Capacitor 10-1780 £0.12
    2. 3x Diode 1N4148 47-3308 £0.008
    3. LM358 (N?) 82-0258 £0.22
    4. An Led (see below)
    5. 2x RTRIM64W Resistor. see below
    6. 7x10k resistor (multipack) £2.28
    7. BD437 81-0102 £0.18
    8. 1 x Some resistor
    9. 1 x 1k Resistor 62-6352 £0.70 for 10
    10. 1 x 1R Resistor 62-6320 £0.70 for 10
    11. 6V PSU
    4. - I assume that any ordianry LED will do, unless theres something ive missed.

    5. I need help on these, im hoping these will work

    8. As I dont know what diode I will be getting this remains some, but specifically how do you calculate the value of this resistor?

    Im intending to make this on strip board which involves me figuring out all the connections. If somebody has a plan the that would be cool. Otherwise im going to try make one myself.

    Silent
    Looks right to me...
    Any LED does do the trick.. its just for indication of power.
    You will need to calculate the proper resistor for the led at teh given voltage.
    That calculation is for the LED only.

    the trims look good..

    Why would you use a stripboard.
    PCB fabrication is really easy.

  10. #80
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    for that rustic home made feel...

    Ive also spotted a error, the 2 capacitors arent the same. Ill adjust the post as soon as Ive worked out the difference.

    PCB fabrication is easy? how so? I thought you need lots of acid and things unless theres a method ive missed?

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